1. Field of the Invention
The invention relates to a drum-shaped scanning unit for magnetic tape recording and/or reproducing apparatus, around whose circumferential surface the magnetic tape can be wrapped at a predetermined angle. Such a scanning unit comprises at least one stationary drum section, a rotatable drum section which is coaxial with the stationary drum section, and a two-part rotary transformer comprising two transformer discs which are made of a ferrite material and which carry at least one transformer winding, the discs being arranged coaxially on the rotatable drum section and on the facing stationary drum section, respectively, with their major disc surface spaced from each other. At least one of the two drum sections is formed with at least three angularly spaced axially parallel bores in each of which a supporting element for the relevant transformer disc, to which said element is connected, is mounted. Such a scanning unit is used in apparatuses for recording and/or reproducing video signals, which are commercially available under the type number VR 2220.
2. Description of the Related Art
In such scanning units the manner in which the transformer discs are mounted onto the drum sections poses a special problem, because the spacing between the facing major disc surfaces of the two transformer discs should be very small, of the order of magnitude of 0.05 mm, in order to ensure an optimum signal-transfer efficiency. Moreover, care must be taken to avoid impermissible changes in the spacing between the two transformer discs as a result of varying operating conditions and aging. Tolerances also play an essential part, because the transformer discs are made of a ferrite material which, as is known, may exhibit comparatively large tolerances when formed into a component. Until now the transformer discs were mounted onto the drum sections by means of an adhesive, but this is a rather intricate method, which also gives rise to stability problems. For mounting a transformer disc on a drum section of the aforementioned known scanning unit the supporting elements are constructed as cylindrical pins which are cemented to the transformer disc with one of their ends and which are inserted into bores in the drum section with their free ends after which they are cemented inside the bores with their circumferential surfaces, which demands several cementing operations.